Polyjuice Problems
by Fiori Omega
Summary: Written for Mi High Lover's polyjuice/body switching competition on HPFC. Sirius and Regulus switch bodies due to a prank gone horribly wrong. Not sure when 2nd round will be given out, so 'complete' for now.
1. Marauders Era Chapter 1

Polyjuice Problems- A series of Polyjuice-induced mix-ups from different eras. First round Marauders.

Marauders Era: Missers Moony, Wormtail, Padfoot and Prongs are planning a particularly peculiar prank on the Slytherins. What happens when the joke goes bad and everything is not what it seems?

"Come on Prongs, one of us has got to test it out, at least before we go all in with it."

"So why don't you?"

"But… my _hair_!"

"Pads… you do realize that your hair's not getting snipped off for the experiment, right? We've already got your hair."

For a moment, Sirius Black, also known as Padfoot, was completely silent. Then he said to his best friend, James Potter, "You know, Prongs, I think we'll do it, then. Though, I may need your help rounding up a single unsuspecting little slime ball."

James's hazel eyes glittered excitedly behind his round glasses. "Shall we?" he asked, motioning out the door.

Sirius grinned and swept James a curtsey before exiting through the door that James held open.

The two other boys in the room looked at each other.

"You know, Wormy," said Remus Lupin, "It's really a wonder that they don't know why people think they're secretly gay." Peter Pettigrew burst into laughter, which James and Sirius skillfully ignored as they left.

"Secretly gay together," Sirius scoffed as the two descended the stairs, "Honestly, you share one drunk-off-your-arse kiss, and then everyone just assumes things. I've snogged loads of girls, but no, people think I'm going for you of all people. Hmph, you're not even that good looking."

James smacked him. "Oi, I'll have you know that I am the most sought after bloke in the entire school."

"Yeah, because all the girls know that I'm way out of their league." Sirius flipped his hair over his shoulder exaggeratedly.

"Either that or they know that you're secretly in love with me," James joked.

Sirius was about to retort, when he suddenly snapped into complete silence. "Prongs, d'you hear that? Sounds like an ickle snakey is slithering on through."

James grinned, "I'll be right back. You get ready with the potion." He disappeared around the corner without a sound.

Sirius measured out a small dosage of the Polyjuice potion into a small vial, and sniffed it curiously. He wondered what it would taste like before anything was put into it. It smelled fine…

Without thinking further, he took a small sip. It was absolutely awful, but he forced it down. Deciding to return to the original plan, he removed a few hairs from the pouch in his pocket and added them to the vial. The potion sizzled for a few seconds before it turned a dark red in color.

Suddenly, James was back, dragging a body. Sirius triumphantly held out the vial, and James grabbed it and dumped it down the struggling student's throat unceremoniously.

Almost instantly, the body became larger, the hair lengthened, and the kid stopped squirming.

Sirius felt very dizzy. "Pads?" he heard James say, "Padfoot, you okay?" Then everything went black.

When he woke up, Sirius was sore all over, but he still sat up quickly. Where the hell was he? He swept his eyes over everything he could see.

It looked like he was in the chamber behind the tapestry on the fourth floor. There were James and himself, as Remus was there too -wait, Sirius had seen himself? There was no mirror back here.

"Moony, Prongs, what's going on?" He croaked through his dry throat."Why am I sitting over there, and why am I tied up?"

"Merlin," Remus whispered. "He doesn't realize what's happened."

"What, in the name of Merlin's bloody left testicle, is happening?"

When James replied, his voice was tense. "What did you do before you prepared the Polyjuice?"

Oh, hell. "I may have… tried some before adding the hair…" he admitted hesitantly. "Why? What's that going to do?"

James smacked his head with his fist as Remus pulled out a pocket mirror. "Why don't you see for yourself?" he asked.

Sirius, not being one to ever pass up the opportunity to see his beautiful face, took the mirror and eagerly looked into it. What he saw staring back at him, however, was not _him_. Instead, the face of his younger brother Regulus, was peering back at him with a mixture of shock and revulsion plainly displayed across his features.

"I look _terrible_!" He cried, jerking his head up to stare in horror at his friends.

"Well," came his own voice, "I'm not too thrilled with my appearance anymore either."

"R-r-Reg? No, that doesn't make any sense. How is this even possible?" Sirius wondered aloud as his body, seemingly with his brother inside got up and started shakily pacing about the small space, which was quite a feat considering his wrists and ankles were bound.

"Well," Remus began conversationally, "It seems as if you two are going to be spending a lot of time getting to know each other before this wears off. And you might want to try and act like each other too, people might get suspicious of 'Regulus' hexing a bunch of Slytherins." He stared pointedly at 'Sirius' before catching himself and glaring towards Sirius in Regulus's body.

"Right, Padfoot, you're kind of on your own for this one, since Regulus is gonna be with us. Why don't you two try and catch up with each other and figure out how to act each other's parts, if you will. See you in a few hours!"

With that, James and Remus ducked out from under the tapestry, sealing it behind them with a muttered charm. James could be heard complaining as they left, "I guess this means no Maraudering for a while, then."

As soon as they'd been sealed in, Regulus had turned to Sirius. "This is all your fault," he said accusingly, "If you wouldn't have been fooling around with things you don't understand, we wouldn't be in this mess. Just like when we were younger, you're always dragging me into trouble."

Though it was hard to see in the gloomy darkness, Sirius scowled at his younger brother. "Me drag you into things? You went and got yourself sorted into Slytherin by yourself, thanks very much."

"And look where being in Gryffindor has got you."

"Girls, fame, popularity, renown, general likability?"

"Kicked out of the house and disinherited, you prat."

"Well," Sirius countered, "I live with the Potters now, and I'm their son. I don't need to bother with our so-called family anymore, and frankly I couldn't care less that I was disowned and thrown out on my sorry arse."

Even through the dark, Sirius could see his brows bunching together in confusion. "Don't do that- you'll give me wrinkles!" he snapped peevishly. Regulus ignored him.

"You really don't care, do you?" he asked quietly.

"I already said that I don't, didn't I?"

For a while, Regulus was silent. Then Sirius saw his own mouth open- and it really was very strange to see your own body conducting its own business without you- and he said rather brusquely, "Anyway, what are we going to do about this little issue of ours?"

Sirius threw his brother's head back and laughed, "Changing the subject, eh Reg? What's the matter, the old folks giving you a hard time? The easy pureblood life not treating you too well?"

As soon as he had started taunting, he was done. A rare, focused demeanor swept onto his (brother's) face as he continued speaking, "Though that is a good question. How are we going to get switched back?"

"I have no idea."

The two brothers sat in silence for a moment, stared through the darkness at each other, met their own eyes in the dim light, and looked away as quickly as humanly possible.

"Well, for a start, Potter and Lupin said that they were going to try to find out what was going on in the library, and see if they could find a way to reverse whatever idiot thing you did."

Sirius shrugged his brother's shoulders, "I suppose that'll have to do for now. In the meantime, what do we do in case it can't be reversed right away? Because I know it'll get suspicious if you only call Prongs and Moony by their surnames."

Regulus in Sirius's body scowled, "Then you'll have to learn to fit into Slytherin. Shouldn't be too difficult, even for you. It is where our family belongs anyway. Well, not that you'd know about _belonging_."

"Good luck in Gryffindor, then," Sirius snarled, "You might have difficulty with the whole bravery, loyalty, and friendship part. I don't think they actual values in Slytherin- what do you have instead? Lessons in cunning, bribery, blackmailing, and the like?- In case you were wondering, Gryffindor can kick Slytherin arse any day." Sirius couldn't help the touch of house loyalty slipping into his voice.

"Ugh, stop that, would you? You've got no clue how downright awful it looks to see someone- especially yourself- wearing Slytherin robes and misguidedly proclaiming the glories of Gryffindor," Regulus said, "It's just terrible."

Sirius smirked, but it didn't feel quite right with his brother's features, so he stopped and allowed the debate over the topic of houses slip. "So… I guess the first thing you should know about Gryffindor is that I- you, I guess, now- only really hang out with James, Remus, and Peter. But you've _got_ to call them 'Prongs', 'Moony', and 'Wormtail'. Though, sometimes I like to find a willing little bint and have a little snog in a broom closet. Er… secondly, don't touch Moony's chocolate if you want to live."

Regulus snorted.

"I'm serious, and more so than in just name, seeing as technically my name is now currently Regulus. Which brings me to another point. Whenever someone asks anyone else in the general vicinity if they are serious, you joke that _you_ are the only Sirius one around. Oh, and flirt with Minnie- that is, McGonagall- for me, will you? Sometimes I think she gets rather lonely with only ol' Dumbledore for company. And you know," he lowered Regulus's voice to a whisper, "I think Dumbledore's gay. So clearly, she's missing out on some love. Other than that and the usual goofing off, I think the other Marauders can help fill you in."

The Sirius Black in front of him rolled his eyes. "Okay, but wait until you hear what you've got to do in Slytherin. And take care that you don't mess anything up for me. Under punishment of death, I swear it, you had better not."

"What are you, our mother? Grating old bitch that she is, that one."

Sirius felt his own stony gray eyes bore into his forehead, "There's a very rigid system in Slytherin. I'm- you are- in the top section, because I'm Bellatrix's little cousin. I'm pretty much the second in command over everything that goes on in Slytherin house behind that fat oaf Slughorn's back. I don't care that you hate everyone in our family- you keep your mouth shut besides for anything that has to do with honoring the Dark Lord or our pureblood standards. If you screw up and they somehow find out you're not me, they're not going to hesitate to kill you, you know."

"Cheerful thought," Sirius said.

"Sorry, I forgot to mention that they'll definitely torture you first."

"Lovely. Just keeps getting all the more charming, doesn't it?"

"But if Bellatrix or Lucius or Narcissa want you to go with them to 'the usual place', don't go. Fake sick or something, anything you can do to get out of it. Trust me. You can't go there or they'll definitely know that you're not me."

"Why not? What's there?"

"I… I can't tell you," Regulus said, "I had to take an Unbreakable Vow. I'll die if I tell you, and then you'll be stuck as me until you die, which probably won't be all that long after."

"How very optimistic of you."

"Well," Regulus countered, "We can't all be merry, goblet-half-full, skipping through the field of honking daffodils, Gryffindors."

"You're going to have to try for the next few days or until whenever this is cleared up if you're going to fit in. And I suppose it'll be my turn to be the sulking, goblet-half-empty, down in the dungeons, Slytherin."

The two brothers scowled at each other from behind the other's face.

"Not that this isn't touching and all," came James's voice as Remus stepped through the tapestry. He followed, running a hand through his unruly hair, "But it's time to go now, so come with us, Sirius. And Regulus, you're on your own again."

All four boys exited the secret passageway, Sirius automatically turning to walk to Gryffindor Tower with the other Marauders, and Regulus turning the other way.

"Oi!" James turned to him and smacked his hand into Sirius's forehead, "Other way, Slytherin slime."

Sirius was stunned for a moment before James spun him around and gave him a push towards where Remus was appearing towing Sirius's body behind him. Right. "Don't touch me, you Gryffindor git," he barked at James, playing along.

James and Remus nodded at him almost unnoticeably in approval. "Later, mate," James whispered.

Sirius stalked away from them, muttering about bloodtraitor filth and thoroughly enjoying the way people stared at him in fear as he passed by giving them all a holier-than-though sneer.

Only when he reached the Slytherin common room did he realize that he had no idea how to get in. Sirius stood there dumbly for what seemed like an eternity before he felt a hand on his shoulder. He tensed and spun around.

"Jumpy, much?" his cousin Bellatrix stood there, her hand still on his shoulder. Her dark eyes glittered with mirth that Sirius had never seen there before. "I was just looking for you. I forgot to tell you earlier, the password's changed. I guess Lucius didn't find you yet either, seeing as you were just standing here like a Hufflepuff."

Sirius forced himself to crack a smile, "So what is the new password?"

"Oh, right, sorry. Here," she turned to face the wall, "Purity."

Perfect. The password practically mirrored his family's motto. He followed Bellatrix through the opening into the Slytherin common room. He flopped down onto a plump green couch, watching as his cousin settled herself into an armchair. "Reg, sit up. How many times have I got to tell you?" she said mockingly, "You'll bring dishonor to the family name slumping around like that!"

When he started to straighten up, alarmed, Bellatrix's face relaxed, and she smirked at him. "Chill out, cous', our parents aren't here." She slouched down in her own seat, still smiling, "You're still pretty easy to wind up."

Sirius stared at her, absolutely stunned. Had she gotten caught in a Polyjuice mix-up as well? With a Hufflepuff?

**AN: Hey, Fiori here. Hope you enjoyed the first chapter of Polyjuice Problems. The next (two?) chapters will also be for Marauders era, before it switches over to whatever my round 2 assignment is. Please review- let me know what you think!**

**-Fiori ^_^**


	2. Marauders Era Chapter 2

Marauders Era: Missers Moony, Wormtail, Padfoot and Prongs are planning a particularly peculiar prank on the Slytherins. What happens when the joke goes bad and everything is not what it seems?

In Gryffindor house, Regulus was having the time of his life.

Far from the strict rulings in Slytherin, he was allowed- and even encouraged to laze around and flirt and joke as he pleased. Maybe being a goody-goody-Gryffindor wasn't so bad after all.

Er… maybe he shouldn't allow himself to entertain such traitorous thoughts. Though it was nice having people immediately jump up to give you a seat by the fire rather than just having your assigned chair that no one else was allowed to sit in. It wasn't that he didn't like having his own personal seat; it was just that somehow this felt more… friendly.

He scooted farther into the comfortable couch before the fireplace. The other three Marauders were all lounging similarly, though Remus was writing an essay, Peter was staring intently at his Charms notes with a confused expression, and James was reading a book titled _Transfiguration: Times and Tales._

Out of all the things he found surprising in Gryffindor was the fact that the Marauders were not, in fact, the completely foolhardy pranksters that everyone seemed to think they always were. They had some of the highest grades and spent time studying and doing homework.

Regulus wasn't sure how they managed to pull it all off- studying, planning out some scheme that would undoubtedly go off without a hitch- as all their pranks seemed to-, writing the several essays assigned each night, then turning around to sneak off to Merlin-knows-where.

As much as Regulus would have liked to let himself completely get into the whole Maraudering business, he couldn't help but think that soon enough he'd be back in Slytherin. _'Where he belonged,'_ added a small, irritating voice in the back of his head.

Well, until he could return to the den of snakes he'd learned to call 'home'- or as much of a home that the strict regime of the Slytherin House could possibly be- he'd just have to make do with being a Gryffindor. Somehow, Regulus wasn't all that concerned with how long it would take to switch back.

He could only wonder how his older brother was faring in the traditional House for their family. Regulus could only hope that Sirius wasn't ruining his reputation too much.

Regulus needn't have worried. Sirius was taking his role as a slimy Slytherin very seriously.

Well, as serious as Sirius could possibly be, in any case. Though he still got twinges of guilt in his stomach when he sneered at the 'Mudblood filth' in the corridors or hexed the innocent little second years for chatting too loud about Gryffindor's chances of winning the Quidditch Cup that year for the fifth year in a row.

He'd never really considered his cousin Bellatrix to be anything except for a maniacal, Dark Arts obsessed, Voldemort crazed lunatic, but it turned out that she was nothing like he'd grown up to see her as around the family. She did enjoy the Dark Arts, and Potions classes, but she liked Transfiguration almost as much as James did.

"So," she'd said to him that night as they were sitting quietly conversing in the common room, "How's your Gryffindor infiltration coming along?" The question was innocent enough among Slytherins, but she'd inconspicuously shot him a wink that had Sirius questioning the actual meaning behind her words.

"Well enough," he'd replied to her evasively, trying to get her to change the subject.

"Really?" Bellatrix had suddenly lowered her voice, leaning in towards him unconsciously, "Then how's _he_ doing? Have you seen _him _lately?"

Sirius wasn't sure who 'he' was, or why she kept putting emphasis on 'his' name, but he was sure that whatever it was, he had to somehow get her to spill. After all, loyalty to Gryffindor House came first, didn't it?

He'd hesitated for a moment before treading cautiously into dangerous conversational territory, "He's fine, for now."

"For now?" Bellatrix's face had lit with an enraged spark, "What do you mean, _for now_? Do you really not care that he could be in danger? Merlin, Reg, I know the two of you havn't exactly been close for a long time, but really- _for now?_ And why wouldn't you tell me about whatever this is before?"

Sirius was suddenly aware that they were talking about himself, who was supposed to be away in Gryffindor Tower at the moment rather than here in Slytherin. "I only meant that… he hasn't been doing many pranks lately. For all I know, they're plotting something big that will get him into trouble." He really hoped the Marauders weren't planning anything too grand without him- He'd kill Prongs later if they were.

"Oh." Like that, the spark had disappeared from Bellatrix's eyes. "So _he_… is alright, then?"

"Yeah," Sirius said softly, "He just keeps getting better."

"Good to hear." Suddenly, Bellatrix stiffened. She added in a slightly louder voice, "So what are we going to do about that dirty Mudblood who got ink on my robes?"

What? Sirius was confused.

"Bella, plotting as usual, I see," drawled a cold voice from behind him that made the hairs on the back of his neck stand up. Lucius Malfoy was standing behind him with his customary frigid sneer securely on his face. Sirius forced himself to nod his head invitingly at the older boy.

"We were just discussing the best ways to make that little shit pay," he explained, as though Lucius hadn't heard Bellatrix's comment, "Got second-rate ink on Bella's best set of robes."

Malfoy's lip curled up in disgust, "Well, I do hope you've gotten one of the little rats to burn them. I hear the contamination only spreads. Yes, the only way to assure cleanliness is to get rid of the more undesirable things once and for all." **(AN: Psst- he's not just talking robes, here. Allusion to blood purity, much? And 'the little rats' are house elves. Yeah, this Lucius is pretty much the epitome of Slytherin slime, as opposed to the darling Bellatrix. You'll see where I'm going with her later, though.)**

Bellatrix nodded in faux-agreement, and Sirius forced himself to do the same. "Couldn't agree more."

This seemed to appease Lucius, and he slunk off to the boys' dormitories, beckoning his cronies Crabbe and Goyle to follow behind him.

As soon as they had disappeared, Bellatrix gave an uneasy sigh, "Honestly, I don't know what Narcissa sees in him."

Sirius could only shrug. He had no idea what drew his cousin to Lucius Malfoy's side, but it seemed that any time he saw Narcissa, she was clutched tightly in Malfoy's arms.

"Just watch," Bellatrix continued, "Right after we graduate, they'll be getting married. And I'll probably have to be the Maid of Honor, or our mum will disown me. Oh, shit, sorry Reg!"

Apparently, Sirius had failed at trying to hide the muted pain that still flashed across his face when there was talk of anyone being disowned or kicked out of their family. "S'okay," he muttered, "I know you didn't mean anything by it."

"Still," she said, "I want to make it up to you." Her face stretched with a smile, the same wild, devil-may-care, smile that Sirius had grown up seeing from her. "How's you and me going to Hogsmeade tonight, then? Havn't done that in a while, now, have we?"

"No," Sirius supposed they hadn't. At least, he and Bellatrix had never gone to Hogsmeade together before, "So, when should we-"

He was cut off by the arrival of a third year girl clutching a scroll with a green ribbon around it. "Bellatrix Black!" she squeaked, thrusting the parchment towards them. His cousin took the scroll and opened it with a roll of her eyes.

"Slughorn," she said, "Hmm, wonder why he wants to see me. Well, I'd better get going, then, but I'll meet you at the Trophy Room at… 10?"

Sirius nodded. He knew he probably shouldn't trust Bellatrix, after all, she was a Slytherin- but then again, so was he, for the moment. His older cousin ruffled his hair as she left for the Potions room, and he smiled at her back as she disappeared.

He slumped back down, closing his eyes for a moment and trying to figure out why he'd never before been able to see this side of Regulus's life, or the Slytherin life, for that matter.

"Oh Reg," a hand smoothed his hair down. Sirius opened his eyes again. Narcissa was perched on the armrest of his seat, looking at him disapprovingly, "Would it kill you to comb your hair? I know you're not as vain as your darling brother, but really. Aunt Walburga would be ashamed." **(AN: Walburga is Sirius and Regulus' mother, according to JKR) **

Sirius scowled at her, purposely shaking his head to muss his hair again. Narcissa just laughed at him.

"Do you know where Bellatrix went?" she asked, "Because I needed to talk to her."

"She went to see Slughorn for something," he told her, "Why, what did you need?"

Narcissa positively beamed, "Just some good news. Our mother sent me a letter, see. So, I have to let her know what's going on. I would tell you, but mum wants me to tell her first, and besides, it involves her too, a bit."

Sirius raised an eyebrow. "I see." This was just like Narcissa- getting someone's curiosity up, and then withholding information to sate the curiosity. It was ridiculous tactics like these that would most likely cause her to be a popular socialite in the future.

Lucius reappeared at her elbow, grasping her hand and pulling it to his lips. "Narcissa, darling, I take it you have not yet found your sister?"

Sirius held back a disgusted grimace. "Well then, shall we all go to find her? She shouldn't be too far- she was only going to Slughorn's classroom."

Lucius regarded him coldly, then motioned for Sirius to follow along as he swept, arm in arm with Narcissa, out the door. For a seventeen year old, Sirius thought, Lucius certainly was quite the bigoted fun-sucker.

The strange party of three found Bellatrix returning from her meeting with Slughorn, a letter clutched tightly in her hand and a huge smile on her face. The smile slipped slightly as her sister detangled herself from her beaux and ran to embrace her, handing her a letter sealed with the Black family crest.

When they pulled back from each other, Narcissa gasped out, "Guess what, Bella! Mum sent me a letter, and they've arranged with the Malfoys that Lucius and I are going to be married in the fall- which is cutting it a bit close, with having to plan everything out for the wedding, but I can't wait- but aren't you excited, Bella? Mind you, you're going to be my Maid of Honor, right?"

Bellatrix embraced her sister again, "Of course, I'd love to Cissy." Sirius could only imagine the look on her face, as it was currently buried in her sister's shoulder, "That's great news." He was pretty sure that he was the only one who heard the flat tone of Bellatrix's voice, even through her praise of her sister's situation.

"Well," Sirius interrupted, "I suppose Bellatrix and I will just have to leave you alone to celebrate and go announce the news to everyone else." He refrained from adding, _as Narcissa will most certainly want to rub it in that she's marrying the handsome, rich Lucius Malfoy,_ and instead smiled innocently.

As soon as the happy couple had retreated back to the Slytherin domain, Sirius turned to Bellatrix. His older cousin's face had fallen considerably as she stared apprehensively at the letter in her hand. "So," he hedged awkwardly, "What did Sluggy want?"

"He informed me that the International Transfiguration Studies Corporation would be most interested in having me join them as soon as I graduate." That had apparently been a dream of Bellatrix's, to join the most renowned Transfiguration league in the Wizarding World. However, to Sirius's confusion, her voice remained flat and emotionless.

Slowly, and with trembling fingers, Bellatrix opened the letter from her mother. Her eyes widened as they raced back and forth, drinking in the information on the single page of parchment. As she neared the bottom of the letter, her eyes darkened and narrowed before shutting entirely.

Sirius slowly approached his cousin, "Bells? You alright?"

"Yeah," she said slowly, "I'm more than alright. I'm engaged." She gave a harsh laugh, "Apparently I'm to be wed to Rodolphus Lestrange within a month of graduation. I guess I'm not going to be joining in with Transfiguration Studies now. Instead, I'll be expected to be little more than a glorified house elf."

"Bellatrix, you don't have to do anything you don't want to, you do know that, right?"

"Reg, I do have to. I'm too far into things to get out now. And I can't end up like Sirius and Andromeda- I'm not like them, Regulus, you know that. I could never stand to be disowned from my family, my Slytherin family. It's all I've ever known." She swiped at her eyes quickly, so fast that Sirius couldn't even be sure that she had done so.

"Just promise me one thing. Never, ever let yourself make the same stupid mistakes that I have. Please."

Before Sirius could respond, Bellatrix had rocked back onto her heels and hurried away. "Go to bed, Reg," she called over her shoulder, seeming more choked up than when a fourth year had accidentally spilt salt over her dinner without her notice.

He just stood in the hallway, utterly stunned. _I guess we won't be going to Hogsmeade, then._

Regulus was sitting with the Marauders in the sixth year's dormitory room. It was the night of the full moon, and the other three boys were steadily growing more antsy by the minute. "Would you idiots relax?" He yelled out finally, "I know he's a werewolf, so stop fidgeting."

Peter fell off the end of his bed. Remus looked shocked. James had the grace to simply cock an eyebrow in confusion.

"Damnit! Does _everyone_ know?" Remus's hands flew to his head and grabbed fistfuls of his prematurely graying hair. "First you three- well, Sirius, James and Peter-, then Snape, then Lily, and now you!"

Regulus swallowed, and looked at his feet. If only he could explain to them that someone other than himself wouldn't have been able to figure it out, that the only reason that he knew was from seeing Fenrir Greyback at the Death Eaters meetings as they grew progressively closer to the full moons.

"I did some… studying on the topic recently. It's not that obvious, you know, so stop worrying so much. It's no wonder that you're looking older already." He couldn't help but reassure the other boys.

James looked like he was considering something, and then after a few seconds of utter silence, he turned toward Remus halfway, "Moony, we should see if he could…"

"You sure?"

"You know how to perform an Unbreakable Vow?" At Remus's nod, James got to his feet and approached Regulus. "We might let you in on a little Marauder secret, that is, if you wouldn't mind," he motioned to Remus, who was holding his wand at the ready, "allowing us to take the necessary precautions."

When Regulus shrugged, he smirked, "Good. Now, envision yourself as Sirius, becoming something inside of himself. It might help to close your eyes."

Regulus wasn't sure if they were trying to play some sort of cruel joke on him, but he shut his eyes anyway. _This is stupid,_ he thought,_ what's going to happen? No, okay, got to think Sirius-ly. Haha seriously, Sirius-ly. Wow, did I really just think that? This whole acting-like-Sirius must really be rubbing off on me._

"Pad- Regulus, open your eyes." James was still standing in front of him, but his head was slightly lower than it had been. Regulus caught sight of himself in the mirror over one of the chests in the room. He was now a large dog roughly the size of a small horse. What the-

"Just a little something we Marauders happen to do about every month or so," James said casually, as if having a huge monstrous dog in the room was an everyday occurrence for them. Though, after this, Regulus wouldn't be surprised at all if it _was_ something that Sirius did every day just for the hell of it.

"Now, for the Vow…"

**AN: Thanks for reading the second installment of Polyjuice Problems: Round One (Marauders Era)! A special thanks to Cutieness (only I wish you were signed in so I could reply to your review instead of needing to delay my thanks until now) and DanceThroughMyStory for reviewing! (And don't worry, there's no James/Sirius. [And sorry to the slash fans] This isn't really a romance fic, so there really are no true 'pairings.' And plus, I'm trying to keep it as realistic as I can, well, at least, at the ending it will all be Cannon.) Anyway, please let me know what you thought of this chapter, and check in for the next (and probably final) chapter of Round One (which should be up before, or at least by, Friday)!**

**-Fiori ^_^**

**(And sorry for the long author's note here!)**


	3. Marauders Era Chapter 3

Marauders Era: Missers Moony, Wormtail, Padfoot and Prongs are planning a particularly peculiar prank on the Slytherins. What happens when the joke goes bad and everything is not what it seems?

**This is most likely the last chapter for this round; however, I may be doing another, very small part just to wrap things up after this. You know, clear some things up, answer questions, etc… (you know, like a Q + A about the story or anything that I've been asked, and an epilogue of sorts). So please leave a question or comment, or something you'd like for me to write a bit on in the wrap up.**

It was really amazing how the Marauders were able to get away with so much.

Without Filch, McGonagall, Dumbledore, or any of the other people that would probably be either patrolling or just wandering around in the halls (as the barmy old Headmaster was most likely doing) noticing the boys, they'd passed through the dark hallways noiselessly.

Almost as if they were simply dark shadows, they'd swept along corridor after corridor; often ducking through passageways that Regulus hadn't previously known existed.

The four of them had even passed Peeves, which made Regulus catch his breath for fear of being caught. Peeves had opened his mouth to start screaming out his usual, 'STUDENTS OUT OF BED, STUDENTS OUT OF BED!' call that was the bane of all night-wandering adolescents at Hogwarts, but James had quickly whispered, "Oi, Peeves, it's us!"

The troublemaking poltergeist had immediately shut his mouth with a soft snap, and then gave a wide smile, tipping his hat and mock bowing as the group passed by. The Marauders had followed suit, bowing so deeply that they were literally bent over, and walking backwards still 'hailing' Peeves.

Once in the deserted Entrance Hall, they'd burst out in hearty yet near-silent chuckles, and crossed to the great double doors that led to the grounds.

James had gotten them to unlock in record time, and in relative silence, before they'd exited the castle. As soon as Peter, in the back of the group, had crossed the threshold, James made a series of complex looking movements with his wand that looked as though they'd been practiced quite often.

The trio of Marauders had then set off purposefully along the grass, Regulus confusedly following close at their heels.

Suddenly, Peter disappeared, and Regulus gave a small yelp of alarm in his shock. Immediately, the remaining two had spun around and trained their wands on Regulus, Remus's pointed at his head, James's directly at his heart.

"Sorry," he muttered, flushing slightly.

James jerked his head towards the massive tree not too far from where they were standing. "Come on," he said, "You might as well transform now."

Regulus took his advice and slowly willed himself to become the great shaggy black dog once more. On all fours, he bounded over to where Remus stood with James as a stag- who towered over them all- and Peter, as a rat was sitting on James's back.

When they reached the Whomping Willow, or, as close to the dangerous tree as they could get without fear of being pummeled, the gigantic stag standing next to him dipped his head and the rat scrambled down the elongated neck to the base of the tree in one swift move.

Peter pressed his small paws to a knot in the roots that Regulus had never noticed before, and the once deadly tree became startlingly docile, the leaves barely fluttering in the cool evening breeze.

One by one, they filed underneath the seemingly frozen branches, and they were in a tunnel, so low that he had to crouch down. Up ahead, Remus was hunched over, and James seemed to be having difficulty moving his antlers through the passage. The only one who didn't seem to be having any problems with mobility in the cramped passageway that was probably just as tall as it was narrow.

After an undeterminable amount of time, they were through and into a room that Regulus was fairly sure he'd never seen before. He'd thought they were going to Hogsmeade, but he supposed that with the Marauders, anything was possible.

Though, he'd had enough nighttime excursions with Bellatrix that he'd been certain he knew the way to get to the village, and everywhere there was to go at Hogsmeade. Apparently not, if this even was part of Hogsmeade village.

There was a sharp ripping noise, followed by muted pops and something that sounded suspiciously like bones grinding together. Regulus was sure that his eyes must be bulging out of his head by now. He'd never seen an actual werewolf transformation, but it was more painful to see than the terrible sight of stumbling across Lucius Malfoy in deep conversation with his own reflection.

Tearing his eyes from Remus's shape-shifting form, Regulus took the opportunity to glance around the room. There were heaps of broken furnishings here and there- a tattered armchair lay on its side, the stuffing leaking out through a series of large slashes. There were chunks missing out of the small end table crumpled in on itself nearby.

With a jolt, Regulus realized that they must be in the Shrieking Shack- the building that had always been 'haunted', the only really haunting thing about it was the purpose it served for a young werewolf struggling to try and blend in with the rest of the magical community.

Regulus didn't know how long it had been, but after a while, the sickening noises stopped and he found it safe to look at the others again. He found the stag, the rat, and a frighteningly large wolf-creature staring back at him.

Nervously, he let out what would have been a cough if he had still been human- a dangerous thing to be around a werewolf- that turned out to present itself as a rumbling bark.

The stag that was James motioned gracefully with his head that they should follow him. He unhooked the latch on the door using his antlers, and they were free to slip out of the shack into the quiet of the night and down into the rest of the village.

As they walked, Regulus looked around. He would probably never get quite used to the sight of Hogsmeade village at night. The lights from the shop window displays lit up sections of the street, every now and again flickering and creating wavering shadows as the four animals passed by.

It really was too bad that he'd have to switch bodies back with Sirius sooner or later, and even more so because he wouldn't be able to tell Bellatrix just how well his brother was doing, because he really was getting quite used to this, and he wasn't sure how well he'd cope with having to go back to Slytherin –and consequently, the Dark Lord- at any time.

Sirius had been looking for Bellatrix all over the castle for the past hour and a half. He'd even searched in the Room of Requirement, though he wasn't sure if Bellatrix even knew about it. Not many people did, but he'd thought it was worth a shot.

He'd finally stumbled across her, literally stumbled, at the top of the Astronomy Tower. His legs had practically given out from underneath him from sprinting all around the castle, and then up the seemingly endless set of stairs, and he'd fallen right next to where she was standing.

"Hey Reg," Bellatrix said in a quiet voice, sitting down beside him and completely disregarding the fact that he was sprawled on the stone next to her.

"Bells," he greeted, fighting to catch his breath, "You okay?"

A sad half-smile twisted her lips, "Yeah, I'm okay. It's fine, you don't have to worry about me."

"Would you, would you still like to go to Hogsmeade?" Sirius questioned, still panting, "It might make you feel better."

At Bellatrix's doubtful grimace, he changed his words, "Or, at least take your mind off of things for a while."

His cousin shrugged, "I don't see why not," she allowed after a short pause, "Shall we?"

The two teens stood together and began to descend the stairs in silence. Neither of them noticed the full moon emerge from behind a group of clouds as they walked away, their backs blissfully ignorant to the dangers that Sirius should have known were lurking.

Surprisingly enough, it seemed that Bellatrix and Regulus also knew about the passageway into the Honeydukes cellar. Bellatrix had whipped out her wand suddenly as they'd been passing the humpbacked witch, and off they'd gone through the passage into the sweet shop.

"So…" Sirius began as they walked slowly through the village streets, "What are you going to do now, if you don't mind me asking?"

"No clue," Bellatrix sighed, shaking her head slowly, "I'll probably just go along with whatever the family wants, now. I'm already in too deep to get out, I think." She sighed again, this time deeper and somehow more saddened than simply resigned. "As are you, probably. We've only been holding off the inevitable, so far."

Sirius looked at her curiously.

"The _Dark Lord_," his older cousin spat venomously, "Has wanted to meet you for a while now. I'd been saying you were too young, but now that you're nearly of age yourself, that's not working anymore. Hence why I've asked you to fake an illness or something whenever we ask you to come with us to the 'usual spot'- he's waiting for you. Apparently our family lineage and spectacular bloodline make us pretty hot commodities for recruiting." The sarcasm in her voice was so thick it was almost cutting.

Suddenly, Sirius's insides turned cold. Lord Voldemort was after his younger brother, had already gotten to their cousin. And what the bloody hell could he do about it? In despair, he grabbed at his hair and tipped his head back to the sky. When he opened his scrunched up eyes, the light from the moon was nearly blinding, and he lowered his head again.

Wait- the light of the moon- the full moon? Sirius's head jerked skywards again, seemingly of its own accord. Sure enough, the round moon hung overhead in the night, the stars twinkling around it as if they were laughing, 'you're screwed'.

"Bella," he said slowly, trying not to panic, "I think maybe we should get ins-"

His words were cut off by a guttural howl as a werewolf appeared on the street corner barely a Quidditch field's distance from where they stood, frozen. Well, shit.

His knees seemed to lock underneath him as he realized that he could no longer just transform into the shaggy black dog that a werewolf would pose no threat to. The breath caught in his throat, and his vision began to go blurry as the werewolf moved steadily closer.

Apparently, in his werewolf form, Remus could sense that Sirius wasn't able to move, so he was taking his time, ambling closer and closer slowly. Where were Prongs and… well, just Prongs, he supposed.

Bellatrix grabbed his hand, dragging him towards the nearest shop, which just so happened to be Zonko's. Remus had apparently noticed this, and was moving quite a bit faster. He was less than a stone's throw away from them when two large dark shapes jumped in between them from only Merlin-knows-where.

At this interruption, Bellatrix promptly fainted dead away. She would have collided with the pavement had Sirius not been able to spontaneously move his arms to catch her. The smaller of the two hulking figures, 'Padfoot' nudged Sirius towards the door, and turned to drag Bellatrix along while Prongs fought Remus off to keep him away from the two non-transformed humans.

When they'd reached the building and entered inside- it was a wonder that it was somehow unlocked- Sirius slammed the door shut behind him and locked it. The dog in front of them morphed into a very concerned looking Sirius Black.

"Hey Regulus," Sirius greeted his own image softly. His younger brother looked at him before turning to their cousin, sprawled unconscious on the floor.

"Is she okay?" he demanded.

"Physically, yeah, she should be alright."

"Only physically? What happened?"

Sirius was unsure of how much to tell his brother, "What do you mean?" he tried to stall.

Regulus lifted an eyebrow at him, "She's tougher than that. One incomplete attack by a werewolf wouldn't shake her like this normally. Something's going on, and you're going to tell me."

As he'd been speaking, Regulus had advanced forward towards Sirius and pinned him against one of the shelves. Normally, Sirius wouldn't have allowed his brother to shake him like that, but Regulus in Sirius's body was larger and more intimidating than Sirius in Regulus's body.

"She's getting married," Sirius squirmed as the shelf behind him dug into his spine, "To Rodolphus Lestrange. That's what's going on. Oh-" he continued as another thought came to him, "What's this I hear about you spying on me?"

Regulus had the decency to look guilty, "Well, I wouldn't exactly say _spying_, more just, ah…" he seemed to be searching for a word that would make it sound better.

"Observing?" Sirius offered dryly, "Keeping tabs on, researching, looking after, following, keeping a one-sided friendship, playing hide and seek but the other person doesn't know it? Pick one- I know them all and I've used them all. Doesn't change what it all comes down to, though."

"Yeah, okay, so maybe me and Bella wanted to see how you were doing. There's no rule against it, anyhow."

"You've really been hanging out with the Marauders too much," Sirius smirked.

"Yeah, that or I was sorted into Slytherin for a reason," Regulus returned with a smirk of his own to rival his brother's.

"So…" Sirius said awkwardly, "How have you been? How are Remus and Peter and James?"

"I've been… well. And Moony, Wormtail, and your boyfriend are good too."

"James is _not_ my _boyfriend_!"

"Funny, though, that you have to keep denying it. I've had to do that several times already- I think I lost count around roughly five thousand," Regulus deadpanned, "and I've only been you for a month!"

Sirius stuck his tongue out at his brother, "Still, it's good to see you again. Though, I think over the past few weeks, I've seen _way_ too much of you, and far too little of myself."

Regulus snorted.

"What? Oh come on, it's not like you can really blame me," Sirius joked, "I mean, look at me- well, you. But it's my body! Or, well, it was."

His brother chuckled. "It's good to see you too."

Sirius held out his arms and spontaneously dragged his brother into a hug. In his mind's eye, he was transported back to the days before the Hogwarts letters, when the two brothers had been closer than Lucius Malfoy and hair gel.

They stood in their brotherly embrace for a long moment, enjoying the memory of the good times in the past. With a final squeeze, Sirius and Regulus released each other and stepped back.

Sirius blinked. He had another sense of déjà vu; he was once again staring at himself. Only this time, he was not staring at the body of Sirius Black, but at Regulus. It felt odd to see the body he'd been living in for a month looking back at him.

"Reg?" Bellatrix's voice rang out shakily, "Where are you?" Both boys glanced at each other, alarm in their wide eyes. Thankfully, though, her eyes were still closed, and she had a hand over her face, pinching the bridge of her nose.

"Go take care of Bella," Sirius said, "I'll make sure that Remus is far away. Just bring her back to Hogwarts. Make up something about the stress making her hallucinate, or something. I can't let Remus's secret spread any more than it already has." With a small pang of guilt, he remembered the 'prank' he'd played on Snape. But since it was Snivellus, after all, it was only a very, very miniscule little twinge deep in his gut.

Regulus nodded, and Sirius took the advantage of Bellatrix still being quite groggy to kiss the top of her head and slip out the door. As soon as he'd closed the door behind him, Sirius transformed into his animagus form. Couldn't hurt to be careful for once.

When he found the rest of the Marauders, he tried to push all thoughts of his brother and his cousin out of his head so he could concentrate on being with his best friends again. But no matter what he did, for the remainder of the night, he couldn't help but wonder what would happen to Regulus and Bellatrix.

Little did he know, Regulus was thinking much along the same lines about him at the same moment, though he did have to pay slightly more attention to getting Bellatrix safely back to the Slytherin dormitories.

**AN: I know I said that this chapter would probably be up Friday, but stuff came up on Thursday and Friday where I couldn't complete the chapter. So, I'm hoping you'll like this chapter, even though it was written more or less halfway during 'reasonable'/daylight hours, and completed sometime in the early morning hours. Please leave a review with a comment or question of any sort (and I mean ANY. I get bored easily, so sue me.) And stay tuned for the next round- should probably be in a week or so.**

**-Fiori ^_^**


	4. Marauders Era Epilogue

Marauders Era: Missers Moony, Wormtail, Padfoot and Prongs are planning a particularly peculiar prank on the Slytherins. What happens when the joke goes bad and everything is not what it seems?

**AN: And now onto the epilogue-of-sorts. A collection of (100 word) drabbles:**

Regulus stood by Bellatrix's side, where she stood shaking in her wedding gown, trying to calm his cousin. "Shh, Bells, it's okay. Or, it will be soon enough. Just try not to think about it too much."

"I don't love him, you know that, Reg. And I wish Sirius and Andromeda were here, even just so I could see them one last time before I go walking to my doom."

Even one month was too much for her to have spent with Sirius, Regulus mused; she was trying to joke around in dire circumstances- such a Sirius thing to do.

The Marauders stood together watching a group of Slytherins scurry past.

"I take it you'd rather not prank _them_ now?"

Sirius nodded at James's question, "But I think Hufflepuff could use some… excitement."

James dipped his head thoughtfully, seemingly in agreement, "Right, so we'll use the Polyjuice and actually pull this one right, yeah?"

Sirius stuck out his tongue, "No, I won't mess it up this time- once is way more than enough."

"But you and Regulus are on better terms now, so that's good. Hey- do you think it'd work with me and Evans?"

Sirius just rolled his eyes.

Where was Regulus? They'd officially joined the Death Eaters together a short while ago, and now he had just disappeared.

Bellatrix didn't know what she was going to do without her cousin. They'd been closer than Bellatrix and her husband- and she was magically _bound_ to Rodolphus.

Regulus had been the only thing keeping her sane in the midst of the madness that was the 'Dark Lord's regime. What was she supposed to do now?

She assumed his death had something to do with the aurors, and so she would avenge herself on them. Bellatrix let out a cruel laugh.

**(AN: In case you didn't quite catch that, that's where Bellatrix goes insane. And also why she killed Sirius, indirectly. He was an auror in the Order of the Phoenix, so she held him with those responsible for killing Regulus. Obviously, she never knew what'd actually killed her beloved cousin.) **

The last thing Sirius thought before he fell through the veil was that he was glad to see Bellatrix again. He couldn't help his laughter, remembering the carefree times when they'd been children 'dueling' with sticks. Then he'd died.

It was nothing like he'd imagined- Sirius was standing in the Slytherin common room, staring at the reflection of Regulus in the mirror. Only when Regulus smiled at him did he realize it wasn't his reflection; his brother was standing behind him.

With no words, the brothers embraced each other, and James and Lily appeared. Sirius had never been so happy.

As Molly Weasley shot a curse at her, Bellatrix couldn't help the laugh that escaped her. It was her turn to embrace death, finally, and she'd been waiting for it.

She'd been killing Order members, aurors, muggles, and almost anyone she came across for so long she'd almost given up hope of ever joining Regulus.

For a moment, she worried for Narcissa and Andromeda, but then she smiled as her eyes closed. Her sisters had their respective son and grandson to keep them going.

Bellatrix opened her eyes to swirling white mist, and saw her cousins running to greet her.

**AN: Well, that's the end of the Marauders part. I tried to keep it as book-complacent as possible, but I can't guarantee anything for the Trio. Anyhow, please review and let me know what you thought!**

**-Fiori ^_^**

_(P.: Each of the five drabbles are 100 words exactly, and my author's notes (excluding this post script) add up to 100 words all together as well! Win!)_


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